The present invention relates to a method of achieving a preferential flow distribution in a horizontal well bore.
The pressure drop along a producing section of well bore has become the subject of study as the technology has been developed to drill horizontal well bores several kilometres long. In an article published in 1990 through the Society of Petroleum Engineers Ben J. Dikken presented an analytic model to predict the frictional pressure drop in a horizontal well due to turbulent well bore flow. In an article published in 1994 in the Petroleum Science and Engineering Journal, Michael J. Landman discussed how productivity of a well can be optimized by varying the perforation distribution along the well. An optimization strategy was proposed in which the perforations were arranged to provide for a uniform specific inflow along the horizontal well bore. Although it was acknowledged that the strategy would result in a slight loss if total well rate, this was justified on the basis that an advantage would be gained in delaying local cresting of water or gas into the well bore from a nearby aquifer or gas cap. The Landman article predicted that as a greater understanding was gained that other selective perforation strategies would be developed.
The present invention relates to a method of achieving a preferential flow distribution in a horizontal well bore.
According to the present invention, there is provided a method of achieving a preferential flow distribution in a horizontal well bore. This method consists of the step of positioning in a horizontal well bore a slotted liner having a plurality of slots which provide a flow area. The slot open flow area of the slotted liner varying along its length in accordance with a selected strategy of flow distribution.
The teachings of Landman related specifically to perforations. In contrast, the present invention relates to slotted liners used to reduce the inflow of sand into the well bore. This method of flow control has an advantage over the teachings of Landman Using the slotted liner for flow distribution is closer to the point of production and has fewer xe2x80x9cdeadxe2x80x9d zones.
Although beneficial results may be obtained through the application of the method, as described above, even more beneficial results may be obtained when the slot open flow area of the slotted liner increases from the heel portion to the toe portion to create an overbalanced condition designed to promote higher flow at the toe than at the heel. This is in accordance with a flow distribution strategy intended to restrict water coning and gas break through tendencies to the toe portion of the well bore where they can be more readily mitigated. For injection wells, the strategy of creating an overbalanced condition is intended to reduce the tendency for short circuiting.
Landman described an unequal flow distribution that occurs in a horizontal well due to such factors as frictional pressure drop and turbulent flow described by Dikken Landman sought to optimize the flow distribution, by making the flow distribution equal along the horizontal well bore. Unlike the strategy advocated by Landman, the strategy described abrade does not seek a uniform inflow or outflow pattern. Instead, an unequal flow distribution is deliberately created. This method has an inherent disadvantage in that higher pressure draw down is required to promote the desired inflow distribution. This means the method is best suited to lighter oil reservoirs with good pressure drive. It is believed that this disadvantage is more than offset by the advantages. Firstly, there is a reduced volume of produced water, with the associated treatment and disposal costs. Secondly, increased reserves are realized from increased cumulative production. This combination of increased recovery and decreased costs will increase the economic life of the well.
Water coning or gas break through inevitably occurs. However, in accordance with the teachings of the present method water coning or gas break through problems can be dealt with. Following the teachings of the method ensures that water coning or gas break through occurs at the toe portion of the well bore. When such water coning occurs a further step is taken of positioning a plug in the toe portion of the well bore in order to isolate the toe portion and permits oil to continue to be produced from that portion of the well bore not experiencing such water coning or gas break through.
Eventually water coning or gas break through will reoccur. Following the teachings of the method ensures that the reoccurrence of water coning or gas break through will be at the remote end of the well bore just ahead of the plug. This can be dealt with by repositioning the plug in the well bore in order to isolate the water producing zone and permit oil to continue to be produced from that portion of the well bore not experiencing water coning or gas break through. In this manner the shut down of the well due to water coning or gas break through can be delayed for years, by merely plugging off the remote end of the well bore.